Java, A Beginner's Guide, 5th Edition, 5th Edition

Type Wrappers

As you know, Java uses primitive types, such as int or double, to hold the basic data types supported by the language. Primitive types, rather than objects, are used for these quantities for the sake of performance. Using objects for these basic types would add an unacceptable overhead to even the simplest of calculations. Thus, the primitive types are not part of the object hierarchy, and they do not inherit Object.

Despite the performance benefit offered by the primitive types, there are times when you will need an object representation. For example, you can’t pass a primitive type by reference to a method. Also, many of the standard data structures implemented by Java operate on objects, which means that you can’t use these ...